The invention relates generally to a twist-tie and more particularly to a non-metallic closure device that can be mechanically twisted to releasably seal containers, including those that are heated in a microwave oven.
Conventional twist-ties are formed with a wire core enclosed in either a plastic or a paper ribbon. These ties are useful because they can seal bags and other containers by hand or machine and the bags can be opened and resealed easily. The metal core tie does not retain memory for any prior shape and will retain the configuration to which it is deformed. Metal core twist-ties are also beneficial because the tie can be twisted and untwisted many times into many different configurations without breakage.
A conventional metal-core twist-tie 400 is shown in FIG. 4. Twist-tie 400 is formed by coating a wire core 1 with a pair of plastic films 2a and 2b. An example of twist-tie 400 is sold under the trade name VINYL-TIES. Plastic ties and paper ties which are formed by covering a core material with a film such as PVC, PET, polyethylene or paper are also common. Another plastic wire tie is described in Japanese Utility Model Publication No. 190654/85.
Metal core twist-ties also suffer from drawbacks. The metal core can protrude from the coating and can injure a user or puncture the container the tie is intended to seal. The metal can rust when exposed to moisture or corrosive materials. Metal closures are also inappropriate for sealing food containers that are intended to be heated in microwave ovens or which are passed through metal detectors.
There have been several attempts to produce non-metallic twist-ties that possess the advantages of a metal core twist-tie without the associated disadvantages. However, such metal-free twist-ties have not proved to be fully satisfactory.
Japanese Application No. 59-79252, filed May 29, 1984, describes a twist-tie formed with a polymeric core disposed between two polymeric tape ribbons. However, it is disadvantageous to form a three piece tie because separation can occur between the core and the ribbon laminate. Furthermore, the properties of the twist-ties formed in accordance with that application were not sufficiently suitable for a wide range of uses. Ties having a core adhered to laminate strips have drawbacks. The laminate must be adhered to the core and this complicates the manufacturing process. The core can separate from the covering and puncture containers or injure a user.
Another non-metallic polymeric twist-tie is described in U.S. Pat. application No. 4,797,313 dated Jan. 10, 1989. That application describes the benefits of including particulate rubber impact modifiers and polymeric material having glass/rubber transitional behavior at a temperature range of about 10.degree. to 40.degree. C. exhibiting yield at a stress between about 500 and 9,000 psi at a strain rate between 0.1 and 0.5 inches per inch per minute. However, such a twist-tie has also been found to be not fully suitable for certain applications.
Accordingly, it is desirable to develop an improved twist-tie which avoids the shortcomings of the prior art.